Interplanetary and interstellar travel have long been the stuff of science fiction, but recent advances in technology have made it possible to explore the possibilities of such journeys. Interplanetary space flights or interplanetary trips are trips with or without a crew between stars and planets, generally within a single planetary system. In practice, space flights of this type are limited to traveling between the planets of the Solar System. All the planets in our solar system orbit the Sun.
Planets that orbit other stars are called exoplanets. Exoplanets are very difficult to see directly with telescopes. They are hidden by the brilliant glare of the stars they orbit. Planets are large natural objects that orbit or travel around stars. Eight planets orbit the star called the Sun.
In order from the closest to the Sun, these planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. The solar system is the collection of the Sun and the objects that orbit around it, including the eight planets. Although these requirements are still far below the requirements for interstellar travel on human time scales, the study seems to represent a reasonable reference point for what could be achieved within several decades, making it not impossible to overcome the current state of current technology. Rockets that obtain their energy from external sources, such as a laser, could replace their internal energy source with an energy collector, which could significantly reduce the ship's mass and allow for much higher travel speeds. Smaller Earth-like planets are much harder to find because they only create small oscillations that are difficult to detect.
Light in a vacuum travels about 300,000 kilometers (186,000 miles) per second, so 1 light-year is equivalent to about 9,461 × 1012 kilometers (5,879 trillion miles) or 63,241 AU. The universe would appear contracted in the direction of travel to half the size it was when the ship was at rest; the distance between that star and the Sun would appear to be 16 light years as measured by the astronaut. However, despite the challenges, a wide range of scientific benefits are expected if interstellar travel becomes a reality. Early studies include the Daedalus Project, carried out by the British Interplanetary Society between 1973 and 1978, and the Longshot Project, a student project sponsored by NASA and the United States Naval Academy, which was completed in 1988. The speeds needed for interstellar travel throughout human life far exceed those that can be provided by current methods of space travel. NASA has been researching interstellar travel since its formation, translating important articles into foreign languages and conducting the first studies on the application of fusion propulsion, in the 1960s, and laser propulsion, in the 1970s, to interstellar travel.
Landis, from NASA's Glenn Research Center, says that a laser-powered interstellar sailboat could be launched within 50 years. Interstellar space is not completely empty; it contains trillions of icy bodies ranging from small asteroids (Oort cloud) to possible rogue planets. Because of the immensity of these distances, non-generational interstellar travel based on known physics would have to occur at a high percentage of the speed of light; even so, travel times would be long, at least decades and perhaps millennia or more. In addition, once travelers arrive at their destination (by any means), they will not be able to travel to the surface of the target world and establish a colony unless the atmosphere is not lethal.
